Hitherto, in a battery control system such as in an electric vehicle, a secondary battery such as a lithium ion battery which can be repeatedly charged and discharged has been used as a battery which supplies electrical power to the battery control system. Then, since such a battery control system demands high electrical power, a battery unit is used in which plurality of secondary batteries are connected in series to each other (hereinafter, referred to as a “battery module”) and plurality of battery modules are further connected in parallel to each other.
For example, in the electric vehicle, a battery pack which includes an assembled battery (hereinafter, the assembled battery will be referred to as a “battery unit”) and a battery management unit (hereinafter, the battery management unit will be referred to as a BMS) with a CMU and a BMU managing the battery unit is disposed at a predetermined position inside the vehicle, and a vehicle-side controller which serves as a high-order system control unit (hereinafter, the vehicle-side controller will be referred to as a vehicle ECU) communicates with the BMU so as to control the charging and discharging operations of the battery unit.
Furthermore, PTL 1 discloses a technique relating to the battery control system on which the battery unit is mounted. According to PTL 1, a control circuit 4 (a battery control unit 10 and a vehicle control unit 11) which serves as a high-order system and is mounted on a hybrid vehicle monitors the current at the time of charging and discharging the battery unit.
Then, when an abnormality is detected in any one of the respective battery modules constituting the battery unit, the control circuit 4 performs a control in which the battery module in which the abnormality is detected is disconnected, thereby preventing the entire battery unit from becoming unusable.